The present invention relates to a pump, especially for conveying construction materials, such as concrete mix or the like. Such pumps comprise a rotary piston rotatable in a housing and provided with radial slides which are controllable by means of a cam disk either connected to the housing or forming a unit with the housing, said cam disk controlling the radial slides mechanically or by means of a hydraulic system to adjust the position of the radial slides.
German Patent Publication (DOS) No. 19 11 852 discloses a concrete pump having a rotor or rather a rotary piston as well as rotary slides corresponding to the radial slides mentioned above, whereby these slides are controllable in the radial direction by means of stationary cam disks or curved disks.
It is a disadvantage of the known pump construction that the take-in space is not properly sealed relative to the actual conveying channel. Even where the radial slides or the housing have been subjected to minor wear and tear, the concrete mix begins to desegregate because the liquid component tends to separate from the solids as the liquid component may flow back. Stated differently, the water or the cement slurry tends to flow back into the take-in chamber. Thus, the conveyed concrete mix becomes drier and drier so that it does not correspond any more to a given quality requirement.
In this context, reference should also be made to German Pat. No. 68 09 17 in which the radial slides are pivotally connected to a control lever for controlling the radial slides. The control lever is supported in a double lever manner at one end of a pressure lever which is rotatably secured in the rotary piston. The free end of the control lever is provided with a guide roller which rides in a guide groove, which in turn is provided in a stationary disk. This type of arrangement of the radial slide control is rather complicated and it may be assumed that a safe operation cannot be provided by this type of structure, due to the entry of portions of the slurry into the radial slide control, and further in view of the fact that the apparatus must work under rough operating conditions.